Add IDR analysis

[drpatelh]

Would be nice to add the IDR analysis that is currently carried out by the ENCODE pipelines:
https://github.com/kundajelab/atac-seq-pipeline
https://docs.google.com/document/d/1f0Cm4vRyDQDu0bMehHD7P7KOMxTOP-HiNoIvL1VcBt8/edit

Another implementation in NF:
https://github.com/DoaneAS/atacflow

ENCODE ATAC-seq Guidelines:
https://www.encodeproject.org/atac-seq/

Amongst other things, this will probably also involve creating pseudo-replicates by merging and equally sampling alignments across replicates.

[drpatelh]

As it stands bioconda::idr and bioconda::macs2 wont build in the same environment because they are built with Python 3 and Python 2, respectively.

https://anaconda.org/bioconda/idr/files

https://anaconda.org/bioconda/macs2/files

Need a workaround for this.

[ewels]

MACS2 Python3 support is hopefully coming... macs3-project/MACS#242 (comment) (though there have been threads around this since 2017, so not sure when..)